The present invention relates to a contactless signaling device. Many prior art devices have been produced in the past. A typical prior art structure is composed an electro-magnetic coil, a moving member or armature that is caused to move by the coil and a bell gong or a horn diaphragm. The action of the moving member in striking the gong or diaphragm causes sound to be emitted. When these electro-mechanical devices are operated from direct current, contact means are provided for the intermittent or interrupted application of the DC power to the coil of the solenoid. In the prior art, it has been customary to use a set of mechanically operated electrical contacts that are closed when the signal is at rest and which open in response to the activation of the reciprocating mechanism or armature.
The prior art mechanically operated electrical contacts have a variety of well known disadvantages. The contacts must be capable of interrupting the peak current to the solenoid. Also, the adjustment of the mechanically operated electrical contacts relative to when they make and break or close and open relative to the motion of the reciprocating member is often critical.
One of the primary disadvantages of the prior art mechanically operated electrical contacts is that after a period of time they sometimes become inoperative or may stick or weld together. Sometimes a particle of insulating matter or other type of ambient particles may become interposed between the contacts, causing the current to stop flowing in the signaling device. When this occurs the signaling device stops operating.
A prior art device is shown in U.S. Pat. No. 4,335,418. This patent discloses an electronic driving circuit in which the discharge and subsequent recharging of a capacitor provides the timing for the interruption of current through the solenoid coil. A set of mechanical contacts is employed to discharge and, alternatively, allow the recharging of the capacitor.